The present invention relates to a highly-drawn and blow-molded polyester bottle having a thin-wall but having no uneven wall-thicknesses and no undesirable whitening appearance. In a further aspect, the present invention relates to a method of manufacturing of these polyester bottles.
Well-known in the art, before the present application, are bottles which have a low yield point and which are obtained by biaxially drawing and blow-molding a preform made of polyethylene terephthalate resin (PET) with the use of a device employing a drawing bar for forcibly drawing the preform in its heightwise, or vertical, direction. For example, Japanese Examined Patent Publication No. 49-3073 discloses a bottle which is biaxially drawn and which is blow-molded from polyethylene terephthalate resin. Japanese Examined Patent Publication No. 58-37895, Japanese Examined Patent Publication No. 61-58288, Japanese Examined Patent Publication No. 61-32978 and Japanese Examined Patent Publication No. 61-56086 concern methods and apparatus for blow-molding with the use of a drawing bar. Japanese Examined Patent Publication No. 62-6970 teaches a method of manufacturing a high-drawn bottle. Japanese Laid-Open (Kokai) Patent No. 64-85733 discloses the crystallization of the bottom of a bottle. However, the manufacture of a bottle which is biaxially drawn and blow-molded using only pressurized fluid in a substantially unconstrained condition has not yet been disclosed in a sufficient manner to make production thereof feasible. Further, there have not yet been described bottles having a high yield point and bottles which are unconstrainedly drawn and molded and in which the wall-thickness of the bottle is substantially uniform except for the port neck section while the ratio of the difference between the wall-thickness of the thickest part and that of the thinnest part to the wall-thickness of the thickest part is less than 50%, and further, wherein the bottle wall other than the part which has been thermally crystallized is highly oriented and crystallized.
Prior known biaxially drawn polyester bottles produced by use of the above-mentioned drawing bar have such disadvantages that they have a low enlargement factor of drawing and many uneven thicknesses. Accordingly, known bottles have been unsatisfactory since they have non-uniform strength and a low strength. The known bottles inevitably have a large wall thickness which increases the occurrence of undesirable whitening or opacity.